While FBI maintains a sizeable confidential human source (CHS) programme – shelling out an average of $42 million in payments to informants each year – it is overseen by an understaffed team of just a few individuals backlogged with requests to vet the credibility of existing CHSs, according to a 2019 Department of Justice inspector-general audit.

Since many CHSs have themselves been charged with serious crimes – often the basis of their cooperation – this can pose serious risks as to their reliability.

The report drew particular attention to the bureau’s insufficient vetting of its long-term sources who can become overly familiar with their handlers and compromise their sense of objectivity. The audit cited as an example of the infamous case of mobster-turned-informant Whitey Bulger, who had grown so close to his FBI handler that he tipped him off prior to his arrest.

The scandal spurred a review of the attorney general’s CHS guidelines, which now require the FBI to revalidate long-term CHSs at regular intervals. The report found the FBI was not in compliance with these guidelines.

In the case of the FD-1023 involving the Bidens, the FBI initially cited source protection as a reason not to share the document with Congress. Yet the secrecy the FBI says is necessary to protect sources can also obscure the credibility of the source. Ironically, one of the sources at the heart of the now discredited Steele dossier, which included explosive allegations about then-candidate Donald Trump, was a confidential human source for the FBI.

Igor Danchenko, the dossier’s primary sub-source whom the US government likewise deemed credible, continued to serve as a CHS from 2017 through 2020, with the FBI paying him over $200,000. Top Republicans, including Grassley, then a ranking member of the Senate Judiciary Committee, excoriated the bureau for its reliance on “unverified” allegations to launch their probe into Trump.

The secrecy the FBI says is necessary to protect sources can also obscure the credibility of the source. Still, top Republicans are now citing exactly the kind of evidence – a confidential human source relaying the unverified allegations of a Ukrainian business executive – that they dismissed as unreliable when it came to Trump and the dossier.

“The FBI created this record based on information from a credible informant who has worked with the FBI for over a decade and paid six figures,” Comer said last week.

Last Wednesday, Comer unveiled a resolution to hold contempt of Congress hearings against Wray, a historically unprecedented course of action that the FBI complained was an “escalation” that was “unwarranted.”

Comer walked back those plans after the FBI agreed to let members of the Oversight Committee review the FD-1023. For civil liberties advocates, the GOP’s recent interest in abuses by federal law enforcement is a welcome if late development.

The FBI has “long abused this privilege to withhold information that’s merely embarrassing to the bureau. … It isn’t partisan politics but rather interest in protecting the FBI from criticism.”

“The FBI has a long history of rebuffing, delaying and refusing congressional requests for information,” Mike German, a former FBI special agent and fellow with the Brennan Centre for Justice’s liberty and national security programme, told The Intercept:

“Obviously, there are some good reasons to withhold information regarding active investigations, investigations not resulting in an indictment, grand jury investigations and source identification, but they have long abused this privilege to withhold information that’s merely embarrassing to the bureau.”

But the bureau’s lack of responsiveness to Congress is not a partisan tendency.

“Sen Chuck Grassley (Republican-Iowa) has been most aggressive in publicising these complaints, but the FBI refuses to cooperate with Democratic members’ requests too,” German said. “It isn’t partisan politics but rather interest in protecting the FBI from criticism.”

In probing FBI Director Christopher Wray about what steps the FBI has taken to check out the information provided in the FD-1023 – much of which can be tested against bank records or by attempting to obtain the alleged audio recordings – House Republicans say they have been told only that the evidence is part of an ongoing investigation.

The FD-1023 makes reference to two other FD-1023s, according to a committee source. On Monday, Comer vowed that he will gain access to additional FBI documents related to the matter. Wray has agreed to allow Comer and Democratic ranking member Jamie Raskin of Maryland, to view them privately, although he has not agreed to open it up to all committee members.

Records like these could provide fodder for additional subpoenas, like the one Comer sent to a Biden family associate on Monday for testimony around his knowledge of the family’s business deals abroad. Comer also said that the committee will be creating new legislation compelling senior elected officials’ family members to disclose more information regarding foreign transactions.

“Moreover, in order to prevent financial transactions from being structured in a way to evade oversight, the Committee is examining whether certain reporting requirements,” Comer wrote in a letter attached to the subpoena, “including any new reporting requirements for senior elected officials’ family members, should extend for a period of time after a President or Vice President leaves office.”

Democrats are highly sceptical that the Trump administration possessed actionable and damning information against Joe Biden but didn’t use it during the 2020 campaign, while Republicans charge the FBI covered up the evidence to protect Biden.

Raskin has argued that Republicans should train their fire on the previous administration because it was the Trump FBI that shut down the investigation. The FBI did indeed close its investigation into the claims made by Giuliani in 2020, but a separate investigation into Hunter Biden is ongoing.

There is some dispute over whether the FD-1023 ever moved from the Giuliani probe to the Hunter Biden one. Wray told Grassley that the document was related to an ongoing investigative matter, according to Grassley spokesperson Taylor Foy. Yet Democrats who have viewed the document said the FBI has told them the investigation into the allegations contained in the document was closed in 2020 after the bureau concluded there wasn’t sufficient evidence to justify continuing with it.

Former Trump Attorney General Bill Barr, meanwhile, told Fox News that the investigation into the specific allegations contained in the FD-1023 was never closed. Rather, Barr said, the evidence was assessed not to be disinformation and forwarded on to the Delaware prosecutor probing Hunter Biden, an investigation that remains ongoing – frustratingly so for Barr. “I think it’s time to fish or cut bait and find out what actually happened in that investigation,” he said.

White House press secretary Karine Jean-Pierre on Tuesday dismissed Grassley’s claim of audio recordings between the Burisma executive and Vice President Joe Biden. “It’s malarkey,” she said.

• A Tell / The Intercept report